Control arrangement for at least two hydraulic consumers

ABSTRACT

The present invention proceeds from a control arrangement for at least two hydraulic consumers which has a positive displacement pump the setting of which is variable by a load-sensing regulator which can be acted on via a load-signaling line by the highest load pressure, on which a maximum-pressure and an output regulation are superimposed, two displaceable metering diaphragms a first one of which is connected between the positive displacement pump and a first hydraulic consumer and the second between the positive displacement pump and a second hydraulic consumer, and two pressure compensators a first one of which is arranged behind the first metering diaphragm and the second behind the second metering diaphragm and the regulating pistons of which can be acted on, in opening direction on a front side, by the pressure behind the corresponding metering diaphragm and in closing direction on the rear side by the pressure in the load-signaling line. In order that the pump pressure does not become maximum, since, upon simultaneous actuation of the two hydraulic consumers, the one consumer is moved against a stop or carries out a clamping function, it is provided that, in the event of such joint control of only the first and the second hydraulic consumers, the load-sensing regulator as from a limiting pressure which lies below the maximum pressure can be acted on by a pressure which is dependent only on the load pressure of the one first hydraulic consumer.

FIELD AND BACKGROUND OF THE INVENTION

The present invention is based on a control arrangement or system for atleast two hydraulic consumers having a positive displacement pump whichis adjusted by a load-sensing regulator responsive to a load-signalingline with the highest load pressure of the plural consumers, on whichthere are superimposed a maximum-pressure and an output regulation. Thesystem includes two displaceable metering throttles, the first of whichis connected between the positive displacement pump and a firsthydraulic consumer and the second of which is connected betweeen thepositive displacement pump and a second hydraulic consumer. The systemfurther comprises two pressure compensators, the first one of which isconnected behind the first metering throttle and the second of which isconnected behind the second metering throttle and, wherein, regulatingpistons of the compensators are activated on a front side by thepressure behind the corresponding metering throttle in an openingdirection and on a rear side of the piston by the pressure in theload-signaling line in the closing direction.

Such a control arrangement is known from EP 0 566 449 A1. It comprises apositive displacement pump which can be so adjusted as to produce at itsoutput a pressure which lies a given amount above the highest loadpressure of all hydraulic consumers. A load-sensing regulator is presentfor this so-called load-sensing regulation which can be acted on by thepump pressure for a reduction of the displacement volume of the positivedisplacement pump and by the highest load pressure and a compressionspring for an increase in the displacement volume of the pump. Thedifference between the pump pressure and the highest load pressurecorresponds to the force of this compression spring.

The pressure compensator which is arranged downstream of eachdisplaceable metering diaphragm maintains the pressure drop over themetering diaphragm constant so that the amount of pressurized fluidflowing to a hydraulic consumer is dependent solely on the opening crosssection of the metering diaphragm and not on the load pressure of theconsumer or on the pump pressure. At the same time, by means of thepressure compensators, the result is obtained that, in a case in whichthe hydraulic pump has been displaced up to the maximum displacementvolume and the stream of pressurized fluid is not sufficient to maintainthe pre-established pressure drop over the metering diaphragms, thepressure compensators of all actuated hydraulic consumers are displacedin closing direction so that all streams of pressurized fluid to theindividual loads are reduced by the same percentage. On the basis ofthis load-independent distribution of flow, all actuated consumers movewith a speed which is reduced percentually by the same value.

A load-sensing-regulated variable displacement pump is ordinarilyequipped also with a pressure regulation by which the maximum possiblepump pressure is pre-established, and with an output regulation whichdetermines the maximum output which can be provided by the pump.Pressure regulation and output regulation are superimposed on theload-sensing regulation.

With a control arrangement of the type described, the following mannerof actuation of two hydraulic consumers is now possible. The onehydraulic consumer is moved up to a stop and is to be held against thisstop. For instance, a clamp which clamps an object fast between its jawscan be moved by the consumer. After the clamping fast of the object,another hydraulic consumer is actuated in order to move the object fromone place to another. The two hydraulic consumers can be present, forinstance, on a mobile working machine, in particular an excavator. Uponthe clamping fast of the object, a pressure builds up on thecorresponding hydraulic consumer, this pressure corresponding to themaximum pressure predetermined by the pressure regulation. Because ofthis high pressure, the output regulation of the variable displacementpump responds even in the case of a small amount of pressurized fluidflowing to the other hydraulic consumer, so that said other hydraulicconsumer can be moved only with a low speed.

SUMMARY OF THE INVENTION

It is the object of the invention so further to develop a control systemhaving the foregoing features so that rapid movement is possible for afirst hydraulic consumer even when a second hydraulic consumer is movedagainst a stop and is to be held fast against this stop.

This object is achieved in accordance with the invention by providingthe control system with a load sensing regulator wherein, upon jointactuation of the consumers, the regulator under a condition of alimiting pressure lying below a maximum pressure is responsive to thepressure dependent only on a load pressure of a first of the consumers.The load-sensing regulator can, in case of joint control only of thefirst and the second hydraulic consumers be acted on as from a limitingpressure lying below the maximum pressure by a pressure which isdependent only on the load pressure of the one first hydraulic consumer.

The invention is based, first of all on the concept that the maximumpressure is not necessary in order to hold the second consumer againstthe stop or to produce the necessary clamping force with the secondconsumer. In accordance with the invention, therefore, a limitingpressure is pre-established below which the pressure in theload-signaling line cannot lie when the second hydraulic consumer isactuated. This limit pressure is sufficient for a pump pressure whichassures the dependable operation of the second hydraulic consumer to beproduced by the pump. If the load pressure of the first hydraulicconsumer lies above the limiting pressure, and if no third hydraulicconsumer is actuated with a higher load pressure, then the pressure inthe load-signalling line is dependent on the load pressure of the firsthydraulic consumer. This load pressure normally lies below the maximumpressure set by the pressure regulation, so that the output regulationresponds only with a flow of pressurized fluid much greater than at themaximum pressure.

Advantageous embodiments of a control arrangement in accordance with theinvention can be noted herein.

In accordance with a feature of the invention, the load-sensingregulator in the case of an individual control of the second hydraulicconsumer can be acted on even above the limiting pressure by the loadpressure of the second consumer.

It is favorable if, aside from the first and second hydraulic consumers,a third hydraulic consumer can also be simultaneously be controlled. Thecontrol arrangement is therefore so developed, in accordance with afurther feature, such that the load-sensing regulator can be acted onalso as from the limiting pressure by the higher of the two loadpressures of the first and third hydraulic consumers.

It is possible to permanently set the limiting pressure in a controlarrangement in accordance with the invention. However, it is morefavorable to set a limiting pressure only in given situations. Inaccordance with FIG. 4, this is suitably done by a displaceable valve asa function of the position of which the load-sensing regulator can beacted on with different pressures. The valve can, for example, bedisplaceable intentionally by hand, depending upon which device isactuated with the second hydraulic consumer. If said consumer actuates,for instance, a shovel on an excavator, no limiting pressure may beprovided. However, if instead of the shovel, a dump actuated by thesecond hydraulic consumer is mounted on the boom of an excavator, thelimiting pressure may be active. Independently of or else depending onthe device to be actuated by the second hydraulic consumer, it isfavorable if, in accordance with yet another feather, the valve isdisplaceable as a function of different actuations of the hydraulicconsumers. In the event of a joint control of the first hydraulicconsumer and the second hydraulic consumer, the limiting value isactive. In the case of a joint control of the first hydraulic consumerand a third hydraulic consumer, or in case of a joint control of thesecond hydraulic consumer and a third hydraulic consumer, the limitingpressure may not be provided.

Furthermore, the limiting pressure may advantageously be set on apressure valve.

A particularly simple construction is possible by the use as pressurevalve of a pressure-limiting valve by which the pressure in a rearpressure space of a load-signaling valve can be limited to the limitingpressure. This load-signaling valve is switched between theload-signaling line and a section of a consumer line which can be actedon by the load pressure of the first hydraulic consumer and has acontrol piston a rear pressure surface of which adjoins the rearpressure space and can be acted on by the pressure prevailing in saidpressure space in closing direction and on a front pressure surface bythe load pressure of the first hydraulic consumer in the openingdirection. Furthermore, the rear pressure space is connected via a chokewith the load-signaling line. The relatively simple construction resultsfrom the fact that the pressure-limiting valve is to be closed only at abore hole in which the control piston of the load-signaling valve iscontained and which is ordinarily accessible from the outside. This isclear also on basis of the directional control valves which are shown inEP 0 566 449 A1 and in the case of which a metering diaphragm, aload-signaling valve, a pressure compensator, two load-holding valvesand a directional control are combined in a housing.

If a pressure-limiting valve is used in an arrangement in accordancewith yet another feature, then the pump pressure lies in each case agiven amount above the load pressure of the first hydraulic consumerwhen the pressure-limiting valve is active and when the load pressure isabove the limiting pressure set by the pressure-limiting valve. Thelatter is ordinarily the case. As has been shown in tests, the pumppressure is also above the limiting pressure but below the maximumpressure when the load pressure of the first hydraulic consumer is lessthan the limiting pressure and when the load-signaling valves arecombined with the pressure compensators in such a manner that theload-signaling line can be acted on via the control piston of thepressure compensator which is associated with the hydraulic load havingthis highest load pressure by said highest load pressure and when,therefore, a construction in accordance with EP 0 566 449 A1 is used.

One particularly advantageous further development of a controlarrangement in accordance with the invention is characterized by thefact that the pump pressure can be limited by a pressure-reduction valveswitched between the flow path to the second hydraulic load and theload-signaling line. This pressure-reduction valve sees to it that, withsimultaneous control of the first and second hydraulic consumers, atleast the limiting pressure prevails in the load-signaling line. On theother hand, it permits the load-signaling line to be acted on by a loadpressure of the first hydraulic consumer or a third hydraulic consumerwhich lies above the limiting pressure. The pump pressure lies in eachcase above the pressure in the load-signaling line by the difference seton the load-sensing regulator.

In a first specific embodiment having a pressure-reduction valve, thisvalve can be arranged in series with the load-signaling valve of thesecond hydraulic consumer. If such a series connection is difficultstructurally to produce, it is then more favorable to arrange theload-signaling valve and the pressure-reduction valve in parallel toeach other and, for the entering into action of the pressure-reductionvalve, to block the connection between a section of a consumer linewhich can be acted on by the load pressure of the second hydraulicconsumer and the load-signaling line. This can be done, for instance, bya 2/2-directional cqntrol valve. However, it may also be favorable forthe blocking to block a movable valve body of the load-signaling valve.

Several embodiments of a control arrangement in accordance with theinvention are shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

With the above and other advantages in view, the present invention willbecome more clearly understood in connection with the detaileddescription of preferred embodiments, when considered with theaccompanying drawings, of which:

FIG. 1 shows a first control arrangement in which a limiting pressurecan be set with a pressure-reducing valve;

FIG. 2 shows a second control arrangement in which a limiting pressurecan be set by a pressure-reduction valve which is arranged between thepressure connection of the positive displacement pump and theload-signaling line, and for the entering into action of which thecontrol piston of a load-signaling valve can be blocked;

FIG. 3 shows a third control arrangement which also comprises apressure-reduction valve which, however, is arranged in series with aload-signaling valve;

FIG. 4 shows the positive displacement pump of the three controlarrangements shown, with three regulating devices constructed thereon;and

FIG. 5 is a section through a segment of a directional control valve,such as can be used in a control arrangement according to FIGS. 1 to 3,in which connection, in accordance with the embodiment shown in FIG. 1,an electromagnetically displaceable pressure-limiting valve can, inaddition, be provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the control arrangements shown in FIGS. 1 and 2, hydraulic oil can bedrawn from a tank 11 by a hydraulic positive displacement pump 10 anddelivered into a pressure line 12 to which a plurality of meteringdiaphragms are connected parallel to each other, a metering throttle 13and a metering throttle 14 being shown in FIGS. 1 and 2. The meteringthrottle can be displaced independently of each other, directly by handor by remote control, for instance electrically orelectro-hydraulically. The metering throttle 13 is associated with afirst hydraulic consumer 15 which is developed as a double-actingdifferential cylinder. The second metering throttle 14 is associatedwith a second hydraulic consumer 16, which is also a double-actingdifferential cylinder.

Each metering throttle 13 and 14 is the speed part of a proportionaldirectional control valve which furthermore includes a directional part17 and 18 respectively, arranged behind the metering diaphragm. Speedparts 13 and 14 and directional parts 17 and 18 respectively are movedjointly and are developed on a single directional-valve slide, as can benoted from FIG. 5.

Between each metering throttle 13 and 14 and the correspondingdirectional part 17 and 18 respectively, there is a 2-way pressurecompensator 19, 20 which has a regulating piston 27 which is movable ina bore hole 21. The piston is acted on in opening direction of thepressure compensator on its front side 23 by the pressure which prevailsbehind the metering throttle 13, 14 in a section 24 of a channel 25, 36respectively leading from the metering diaphragm to the directionalpart. By its rear face 26, which is of precisely the same size as thefront face 23, the regulating piston 22 adjoins a rear pressure space 27which is permanently connected with a load-signaling line 28 regardlessof the position at the time of the regulating piston 22. Theload-signaling line 28 connects together all bore holes 21 into which,as in the embodiments of FIGS. 1 and 2, it debouches in an annulargroove 29 or, as in the embodiment of FIG. 5 in which the regulatingpiston of the pressure compensator is contained in a sleeve which isadditionally inserted into a housing of the directional control valve,into several bore holes 30. The connection between the annular groove 29or the bore holes 30 and the rear pressure space 27 is produced via theregulating piston 22, a throttle 31 the cross section of which is about0.5 mm² being present in the connection.

The regulating piston 22 of a pressure compensator 19, 20 can assume twoend positions, in which connection in the one end position which isshown in FIGS. 1 and 2 and which is established by a weakly prestressedcompression spring 32 present in the pressure space 37, a connectionbetween the section 24 and a section 33 of the channel 25, 26 presentbetween the pressure compensator 19, 20 and the directional part 17, 18respectively is interrupted. In the other end position of the regulatingpiston 22 of a pressure compensator 19, 20, the connection between thechannel sections 24 and 23 is entirely open and the section 24 of thechannel 25, 36 is connected with the load-signaling line 28 via boreholes 34, 35 in the regulating piston. In the connection, the bore hole35 serves as a throttle which is arranged in the regulating piston, theopening cross section of which throttle is substantially greater thanthat of the throttle 31.

The load-signaling line 28 leads to a regulating unit 40 which is builton the positive-displacement pump 10. This regulating unit 40 is knownper se and is shown in further detail in FIG. 4. It comprises three3/2-proportional directional control valves 41, 42 and 43. The pump 10is displaced finally by a setting cylinder 44 having a setting piston 45which is provided on one side with a piston rod 46. In the piston rodthere is arranged a measurement piston 47 which acts, against the forceof a compression spring 48, on a single-arm lever 49. The active leverlength for the force of the compression spring is constant, while theactive lever length for the force of the measurement piston 47 isdependent on the angle of swing of the pump 10. The measurement pistonis acted on by the pump pressure. The pump pressure prevails also in apressure space on the piston-rod side of the setting cylinder 44 withinwhich space a compression spring 50 is arranged which acts on thesetting piston 45 in the direction towards enlargement of the angle ofswing of the pump 10. The valve 43 serves for regulating the output ofthe positive displacement pump 10. It has a connection which isconnected to the tank 11 via a line 51. Another connection is present onthe delivery line 12. The third connection, which can be connected withthe first or the second connection, is connected with a first connectionof the valve 42 by which the pump pressure is limited to a maximumvalue. A second connection of the valve 42 is connected to the pressureline 12 via the pressure space on the piston-rod side of the settingcylinder 44. The third connection of the valve 42 can be connected withits first or second connection and is permanently connected with aconnection of the so-called load-sensing valve 41. The latter has asecond connection, which is permanently connected with the pressure line12, and a third connection which is permanently connected with thepressure space on the piston-rod side of the setting cylinder 44 and canbe connected to the first or the second connection. A slide, not shownin detail, of the valve 43 is pressed by the compression spring 48against the lever 49 and acts to increase the angle of swing of the pump10. A slide (not shown in detail) of the valve 42 is acted on by acompression spring 52 so as to enlarge the angle of swing and by thepump pressure so as to reduce the angle of swing of the pump 10. A slide(not shown in detail) of the load-sensing valve 41 is finally acted onin the direction of an increase of the angle of swing of the pump 10 bya compression spring 53 and the pressure prevailing in theload-signaling line 23 in the direction of reducing the angle of swingby the pump pressure. On the slide of the valve 41 a force equilibriumprevails when a difference which corresponds to the force qf the spring53 is present between the pump pressure and the pressure in theload-signaling line 28. Ordinarily, the difference is about 20 bar.Equilibrium prevails on the slide of the valve 42 when the pump pressureproduces a force which corresponds to the force of the spring 52.Ordinarily, in the case of equilibrium, the pump pressure is in thevicinity of 350 bar.

The load-signaling line 28 is connected to the tank line 51 via a nozzle54. Furthermore, as can be noted from FIGS. 1 and 2, a pressure-limitingvalve 55 is connected to the load-signaling line, the valve being set toa pressure which is below the maximum pressure set on the valve 42 bythe amount by which the pump pressure and the pressure prevailing in theload-signaling line 28 differ upon equilibrium on the slide of theload-sensing valve 41.

In order to explain the manner of operation of a control arrangement inaccordance with the FIGS. 1 and 2 in normal operation, let us assumethat, first of all, the first hydraulic consumer 15 is to be actuatedand that, for this purpose, the metering throttle 13 is opened to agreater or lesser amount and the directional part 17 has been displacedin accordance with the desired direction of movement of the consumer 15.The pressure compensator 19 opens completely so that the load pressureof the consumer 15 builds up in both sections 24 and 33 of the channel25. This load pressure is signaled via the regulating piston 22 of thepressure compensator 19 into the load-signaling line 28 and, via thelatter, acts on the slide of the load-sensing valve 41. There is thusestablished in the delivery line 12 a pump pressure which is higher thanthe load pressure of the consumer 15 by an amount which corresponds tothe force of the compression spring 53. Regardless of the opening crosssection of the metering diaphragm 13, the pressure drop over it isalways the same and corresponds to the difference between the pumppressure and the load pressure of the consumer 15. Since the loadpressure of the consumer 15 is present in the entire load-signalingline, it is also prevails in the rear pressure spaces 27 of the twopressure compensators 19 and 20.

In addition to the consumer 15, the second hydraulic consumer 16 can nowalso be actuated, in which connection let us assume first of all thatthe load pressure of the second hydraulic consumer 16 is less than theload pressure of the first consumer 15. The load pressure of the secondhydraulic consumer can therefore not fully open the pressure compensator20. Its regulating piston rather now assumes a regulating position inwhich the pressure which acts on its front end surface 23, if onedisregards the force of the compression spring 32, is exactly as greatas the pressure in the pressure space 27 and therefore corresponds tothe load pressure of the first consumer 15, and in which there is noconnection between the space in front of the end surface 23 and theload-signaling line 28. Thus the pressure drop over the measuringthrottle 14 is precisely as great as over the measuring throttle 13. Thepressure in the section 24 of the channel 36 drops via the pressurecompensator 22 to the load pressure of the second hydraulic consumer 16.

On the other hand, if the load pressure of the second hydraulic consumer16 is higher than the load pressure of the first hydraulic consumer 15,then, upon actuation of the second hydraulic consumer, the pressurecompensator 20 opens completely so that the load pressure of theconsumer 16 is present in front of the end 23 of this pressurecompensator 20, the regulating piston of the pressure compensator 20opens entirely, and the load pressure of the consumer 16 is signaledinto the load-signaling line 28. The pump pressure increases until itlies above the load pressure of the consumer 16 by the value establishedon the valve 41. The regulating piston of the pressure compensator 19 ismoved into its regulating position.

Thus, in each case the highest load pressure of an actuated hydraulicconsumer is signaled in the load-signaling line 28. The pump 10 producesa pump pressure which is about 20 bar above said highest load pressure.If now, for instance, a clamping device by which an object is grasped isactuated by the consumer 16 and is then to be transported by actuationof another hydraulic consumer, the pump pressure would reach the maximumvalue set on the valve 42 so that, even with only a slight amount offeed, the output regulation of the pump would respond and only a lowspeed of the consumer 15 would be possible. In this case, the maximumpressure of, for instance, 350 bar is far above the pressure which isnecessary for a firm clamping of the object to be transported, which,for instance, lies in the vicinity of 150 bar. In order that the pumppressure does not in such a case increase to the maximum pressure, it isnow provided, in accordance with the invention, in the controlarrangements shown that, upon a joint control of the first consumer 15and the second consumer 16, which exercises a clamping function, theload-signaling line 28 is acted on, as from a limiting pressure lyingbelow the maximum pressure, by a pressure which is dependent only on theload pressure of the first hydraulic consumer 15. For this purpose, inthe case of the embodiment of FIG. 1, the rear pressure space 27 of thepressure compensator 19 can be connected via a 2/2-directional controlvalve 60 to a pressure-limiting valve 61 which is set to a fixed valueof, for instance 150 bar. The directional control valve 60, in itsposition of rest, blocks the connection between the pressure space 27and the pressure-limiting valve 61. In the other switch position inwhich it can be brought, for instance, by actuation with a controlpressure, it establishes a connection between the pressure space 27 ofthe pressure compensator 19 and the input of the pressure-limiting valve61. The directional control valve 60 is brought into its second switchposition when the first consumer 15 and the second consumer 16 areactuated simultaneously. Ordinarily the load pressure of the firsthydraulic consumer 15 lies above the value set on the pressure-limitingvalve 61. In this case, the load pressure of the first hydraulicconsumer is able to open the pressure compensator 23 completely and tohold its regulating piston 22 in its upper end position, shown inFIG. 1. Via the nozzle 35 there is a connection between the channel 25and the load-signaling line 28. The pressure compensator 20 is alsoentirely open, since the pressure in the load-signaling line 28 prevailsin its rear pressure space 27 and, since no pressurized fluid flows tothe consumer 16, the front end 28 of the regulating piston of thepressure compensator 20 is acted on by the pump pressure. In addition toover the metering throttle 13, a small amount of pressurized fluid nowflows over the throttle 35 of the pressure compensator 20, theload-signaling line 28, and the throttle 35 of the pressure compensator19 to the first consumer 15. Between the two throttles 35, and thereforein the load-signaling line 28, a pressure is established which is 20 barabove the load pressure of the first hydraulic consumer 15. Via thethrottle 31 of the pressure compensator 19, this pressure drops to thepressure set on the pressure-limiting valve 61 and prevailing in thepressure space 27 of the pressure compensator 19.

If the load pressure of the first hydraulic consumer 15 is lower thanthe pressure set on the pressure-limiting valve 61, then, as tests whichwere carried out have shown, a pressure which lies above that set on thepressure-limiting valve but is far below the maximum pressure alsobuilds up in the load-signaling line 28.

As alternative to a valve combination which consists of a directionalcontrol valve and a permanently set pressure-limiting valve, apressure-limiting valve which is displaceable, for instance, by anelectromagnet can also be used in order to establish a limiting pressurein the pressure space 27 of the press ure compensator 19. This solutionis shown as an alternative in FIG. 1. In this case, thepressure-limiting valve, which is now provided with the referencenumeral 62, is so developed that, with the electromagnet disconnected,it is set to a value which lies above the operating pressures whichoccur and is shifted to a lower value of, for instance, 150 bar, byactuation of the electromagnet. It therefore ha s a so-called droppingcharacteristic. The force of the electromagnet supports the pressureforce which seeks to open the pressure-limiting valve 62 against theforce of a compression spring. The falling characteristic is favorablewhen the connect time of the electromagnet is shorter than thedisconnect time. In the reverse case, the magnet is so arranged that itacts against the pressure force in the closing direction of the valve62.

In the embodiment shown in FIG. 2, there is used for the establishing ofa limiting pressure, not a pressure-limiting valve but apressure-reduction valve 65 which can be built directly on the positivedisplacement pump 10 and the input of which is connected with thepressure line 12 and its output with the load-signaling line 28. A weakcompression spring 66 acts on a valve body, not shown in detail, in theopening direction of the valve 65. Furthermore, the valve body can beacted on in the opening direction also by an electromagnet 63. When theelectromagnet 63 is disconnected, a very small pressure in theload-signaling line 28 is sufficient to close the pressure-reductionvalve 65. When the electromagnet 63 is connected, a pressure of, forinstance, 150 bar in the load-signaling line is necessary in order toclose the valve 65.

An additional electromagnet 67 is attached to the rear pressure space 27of the pressure compensator 20 and can, by a ram 68, block theregulating piston 22 of the pressure compensator 20 in such a mannerthat, while the latter can open the connection between the sections 24and 33 of the channel 36, it cannot open the connection between thischannel and the load-signaling line 28. The regulating piston of thepressure compensator 20 is blocked when the magnet 67 is connected.

In normal operation, which has been described already above, the magnets63 and 67 are disconnected. The pressure-reduction valve 65 is thereforeclosed already with a very small pressure in the load-signaling line 28and is therefore practically without effect.

Let us now assume that both consumers 15 and 16 are actuated and bothmagnets 63 and 67 are connected. Let us assume that the load pressure ofthe first hydraulic consumer 15 is less than the limiting pressure of,for instance, 150 bar set on the pressure-reduction valve by means ofthe electromagnet 63. Thus, this pressure of 150 bar prevails in theload-signaling line 28 and in the pressure spaces 27 of the pressurecompensator 19 and the pressure compensator 20 with the regulatingpiston 22 blocked by the magnet 67. A pump pressure of 170 bar is builtup which acts on the piston of the cylinder 16 and drops, via themetering diaphragm 13, to 150 bar in the section 64 of the channel 25and, via the pressure compensator 19, to the load pressure of theconsumer 15 in the section 33 of the channel 25.

On the other hand, if the load pressure of the first hydraulic consumer15 is higher than the pressure set on the pressure-reduction valve 65,the pressure compensator 19 opens completely, so that the higher loadpressure of the first consumer is signaled into the load-signaling line28. The pressure-reduction valve 65 is not able to influence thispressure so that a pump pressure lying 20 bars above the load pressureof the consumer 15 is established in the pressure line 12. Aside fromthe consumers 15 and 16, other hydraulic consumers can also be actuated,in which case a pressure of 150 bar or a higher load pressure of theconsumer 15 or of the other hydraulic consumers prevails in theload-signaling line 28.

The control arrangement of FIG. 3 differs essentially in three pointsfrom the control arrangement of FIG. 2. On the one hand, the highestload pressure is not signaled into the load-signaling line 28 via thepressure compensator associated with the consumer with the highest loadbut via a return valve 70 which opens towards the load-signaling line28. Each return valve 70 of the individual consumers, with the exceptionof the second consumer 16, is connected directly to the line section 33between the corresponding pressure compensator and the directional part17. The second difference from the embodiment of FIG. 2 is that apressure-reduction valve 71 is present only in series with the returnvalve 70 associated with the secon d hydraulic consumer 16. Thirdly, anelectromagnet 63 acts, together with the pressure at the output of thepressure-reduction valve 71, on a movable valve body of the valve inclosing direction against a strong compression spring 66 acting inopening direction. The compressio n spring 66 is so strong that thepressure-reduction valve 71 is opened under the operating pressureswhich occur when the electromagnet 63 is disconnected.

The control arrangement of FIG. 3 with the electromagnet 63 disconnectedtherefore functions in the normal manner which has already beenindicated above. If the pressure-reduction valve 71, however, is now setto an initial output pressure of for instance 150 bar, after theactuation of the electromagnet 63, this pressure of 150 bar is signaledinto the load-signaling line 28 provided that the highest load pressureof all other consumers actuated is less than 150 bar. The pump pressureis then 170 bar, which acts on the piston of the cylinder 16 andproduces a given clamping force. If the highest load pressure of theother hydraulic consumers actuated is higher than 150 bar, then theload-signaling line 28 is acted on by this highest load pressure and thepump pressure is 20 bar above this highest load pressure.

If the time during which the control arrangement of FIG. 3 is operatedin the manner last described should be longer than the time of so-callednormal operation, the electromagnet 63 will be permitted to act in theopening direction of the valve 71 and the limiting pressure of, forinstance, 150 bar will be established by a corresponding pretensioningof the compression spring 66. Upon the connecting of the electromagnet63, the valve 71 is then open at all operating pressures.

The proportional-directional-control valve segment of FIG. 5 is providedin a housing 80 with a valve bore hole 81 in which a control piston 82is axially displaceable. This control piston has at its center ametering-diaphragm part 13, 14 and, on both sides of themetering-diaphragm part, in each case half of a directional part 17.

In a stepped bore hole 83 which is aligned vertically with the bore hole81 there is inserted a pressure compensator 19 which contains aregulating piston 22 in a sleeve 84 having the aforementioned bore holes30. Between the pressure compensator and the metering throttle there isthe channel section 24 and between the pressure compensator 15 and thehalves of the directional part 17 there is in each case a part of thechannel section 33, a load-retaining valve 85 being present in eachpart. A connection between the channel sections 24 and 33 can beproduced via several radial bore holes 86 in the sleeve 84. The boreholes 30 extend outwards from an annular space between the sleeve 84 andthe wall of the bore hole 83 into which annular space the load-signalingchannel 28, indicated in dashed line, also debouches twice. Thisload-signaling channel 28 is connected at all times to the rear pressurespace 27 via an outer groove 87 of the regulating piston 22 and via aradial bore hole and an axial hole as well as via a nozzle 31 arrangedin said axial bore hole. With the pressure compensator entirely openthere is furthermore a connection through the regulating piston 22between the line section 24 and the bore holes 30. For this, theregulating piston has another axial bore hole 34, another radial borehole and another annular groove. The radial bore hole can in thisconnection be considered a nozzle 35.

A pressure-limiting valve 62 by which the pressure in the pressure space27 can be limited to a given pressure is screwed, by a threadedattachment into the sleeve 84, closing the pressure space 27. With theelectromagnet 63 connected, the magnetic force acts in the openingdirection of the valve 62 together with the force produced by thepressure in the pressure space 27 on a valve body 88. A strongcompression spring 89 acts in closing direction of the valve 62. Thearmature of the electromagnet 63 is a flat armature which is developedintegral with the valve body 88.

We claim:
 1. A control system for a plurality of hydraulic consumerscomprising:a variable displacement pump having a displacement which isadjustable by a load-sensing regulator, said load-sensing regulatorbeing selectively connected with a load pressure by a load-signalingline, wherein said load-sensing regulator includes a maximum pressurecontrol and a power control; a first and a second adjustable meteringthrottle, the first metering throttle being connected between thevariable displacement pump and a first of the hydraulic consumers, thesecond metering throttle being connected between the variabledisplacement pump and a second of the hydraulic consumers; a first and asecond pressure compensator, the first pressure compensator beingconnected behind the first metering throttle, and the second pressurecompensator being connected behind the second metering throttle; whereineach of the pressure compensators has a regulating piston, the piston ofeach of a respective one of the pressure compensators being acted on,via a front side thereof, by pressure behind the corresponding meteringthrottle in an opening direction, and on a rear side of the piston bypressure in the load-signaling line in a closing direction, a pressurevalve connected with one of said first and said second consumers, andbeing switchable between an active and an inactive state, and when inits active state defines a limit pressure lying below a maximumpressure; the load sensing regulator is acted on by a pressure which isdependent on a load pressure of the first hydraulic consumer when theload pressure of the first hydraulic consumer is greater than the limitpressure and said pressure valve is in its active state; and the loadsensing regulator is acted on by a pressure which is dependent on thelimit pressure when the load pressure of the first hydraulic consumer isless than the limit pressure and said pressure valve is in its activestate.
 2. A control system according to claim 1, wherein in the case ofindividual actuation of the second hydraulic consumer (16) theload-sensing regulator (41) is acted on by the load pressure of thesecond consumer (16) only when the load pressure of the second consumeris above the limiting pressure, when said pressure valve is in itsactive state.
 3. A control system according to claim 2, wherein theplurality of consumers includes a third hydraulic consumer, a thirdmetering throttle, and a third pressure compensator, with the thirdpressure compensator and the third metering throttle connected seriallybetween the pump and the third consumer and the third compensator beinglocated between the third metering throttle and the third consumer forthe supplying of pressurized fluid by the pump to the third consumer;inthe case ofjoint activation of the first, second and third hydraulicconsumer; the load-sensing regulator (41) is acted on by the higher ofthe two load pressures of the first and third hydraulic consumers, whenthe load pressures of the first and third hydraulic consumers aregreater than the limit pressure and said pressure valve is in its activestate.
 4. A control system according to claim 1, wherein:the pluralityof consumers includes a third hydraulic consumer, and the systemcomprises a third metering throttle, a third pressure compensator, and aload-sensing regulator; in a condition of joint activation of theplurality of hydraulic consumers with a supplying of the consumers withpressurized fluid by the positive displacement pump, the third pressurecompensator and the third metering throttle are connected seriallybetween the pump and the third consumer with the third compensator beinglocated between the metering valve and the third consumer for thesupplying of the pressurized fluid by the pump to the third consumer;and the pressure valve is in its active state and both the load pressureof the first consumer and the load pressure of the third consumer arehigher than the limit pressure, the load-sensing regulator being actedon by a higher of load pressures of the first consumer and thirdconsumer.
 5. A control system according to claim 1, wherein theload-sensing regulator (41) is acted on by differing values of pressureas a function of the state of the pressure valve (60, 62, 65, 71).
 6. Acontrol system according to claim 5, further comprising anelectromagnet, and wherein the pressure valve (60, 62, 65, 71) isdisplaceable by operation of the electromagnet as a function ofdifferent actuations of the hydraulic consumers (15, 16).
 7. A systemaccording to claim 1, wherein:each of said pressure compensators has arear pressurized space and a rear throttle disposed in the piston andopening via the rear side of the piston into the rear pressurized space;the load-signaling line is connected via the regulating piston of thefirst pressure compensator to a section of a first consumer line betweenthe first consumer and the first metering throttle to be responsive toload pressure of the first consumer; the regulating piston of the firstcompensator is acted on by pressure in the rear pressurized space movingthe regulating piston in a closing direction, the pressure from the rearpressurized space is selectively communicated, via the rear throttle,with the load signaling line; and wherein the pressure valve is apressure limiting valves which in the active state, limits the pressureof the rear pressurized space to the limiting pressure lying below themaximum pressure.
 8. A control system according to claim 7, whereinload-signaling valves are incorporated into the pressure compensators(19, 20) enabling the load-signaling line (28) to receive a higher loadpressure via the piston (22) of the pressure compensator (19, 20) whichis associated with the hydraulic consumer (15, 16) having the higherload pressure.
 9. A control system according to claim 8, wherein eachload-signaling valve is incorporated into the piston (22) of anassociated pressure compensator (19, 20).
 10. A control system for aplurality of hydraulic consumers comprising:a variable displacement pumphaving a displacement which is adjustable by a load-sensing regulator,said load-sensing regulator being selectively connected with a loadpressure by a load-signaling line, wherein said load-sensing regulatorincludes a maximum pressure control and a power control; a first and asecond adjustable metering throttle, the first metering throttle beingconnected between the variable displacement pump and a first of thehydraulic consumers, the second metering throttle being connectedbetween the variable displacement pump and a second of the hydraulicconsumers; a first and a second pressure compensator, the first pressurecompensator being connected behind the first metering throttle, and thesecond pressure compensator being connected behind the second meteringthrottle; wherein each of the pressure compensators has a regulatingpiston, the piston of each of a respective one of the pressurecompensators being acted on, via a front side thereof, by pressurebehind the corresponding metering throttle in an opening direction andon a rear side of the piston by pressure in the load-signaling line in aclosing direction; a pressure valve being switchable between an activeand an inactive state, and when in its active state, setting a limitpressure lying below a maximum pressure. the load-sensing regulator,upon joint actuation of the first and the second hydraulic consumers isacted on by a pressure which is dependent only on a load pressure of thefirst hydraulic consumer when the load pressure of the first hydraulicconsumer is greater than the limit pressure; and the load sensingregulator is acted on by differing values of pressure as a function ofthe state of the pressure valve.
 11. A control system according to claim10, further comprising an on-off valve connected between the pressurevalve and the first compensator, and wherein the pressure valve (61) hasa fixed setting and is switched between active and inactive states bythe switching of he on-off valve (60).
 12. A control system according toclaim 10, wherein the pressure valve (62, 65, 71) is displaceable by anelectromagnet (63).
 13. A control system according to claim 12, whereinthe pressure set on the pressure valve (62, 65, 71) is lower upon thepassage of electric current through the electromagnet (63) than in theabsence of current flow through the electromagnet.
 14. A control systemaccording to claim 10, wherein the pressure valve (60, 62, 65, 71) isdisplaceable as a function of different actuations of the hydraulicconsumers (15, 16).
 15. A control system according to claim 14, furthercomprising an on-off valve in series with the first compensator, andwherein the pressure valve (61) has a fixed setting and is switchedbetween active and inactive states by the switching of the on-off valve(60).
 16. A control system according to claim 14, wherein the pressurevalve (62, 65, 71) is displaceable by an electromagnet (63).
 17. Acontrol system according to claim 16, wherein the pressure set on thepressure valve (62, 65, 71) is lower upon the passage of current throughthe electromagnet (63) than in the absence of current flow through theelectromagnet.
 18. A control system for a plurality of hydraulicconsumers comprising:a variable displacement pump having a displacementwhich is adjustable by a load-sensing regulator, said load-sensingregulator being selectively connected with a load pressure by aload-signaling line, wherein said load-sensing regulator includes amaximum pressure control and a power control; a first and a secondadjustable metering throttle, the first metering throttle beingconnected between the variable displacement pump and a first of thehydraulic consumers, the second metering throttle being connectedbetween the variable displacement pump and a second of the hydraulicconsumers; a first and a second pressure compensator, the first pressurecompensator being connected behind the first metering throttle, and thesecond pressure compensator being connected behind the second meteringthrottle; wherein each of the pressure compensators has a regulatingpiston, the piston of each of a respective one of the pressurecompensators being acted on, via a front side thereof, by pressurebehind the corresponding metering throttle in an opening direction, andon a rear side of the piston by pressure in the load-signaling line in aclosing direction; a pressure valve connected between the load-signalingline (28) and a second consumer line connecting the pump (12, 36) to thesecond hydraulic consumer (16), and setting a limit pressure lying belowa maximum pressure; the load-sensing regulator, upon joint actuation ofthe first and the second hydraulic consumers is acted on by a pressurewhich is dependent only on a load pressure of the first hydraulicconsumer when the load pressure of the first hydraulic consumer isgreater than the limit pressure.
 19. A control system according to claim18 further comprising a load-signaling valve connected in series withthe pressure valve;the load-signaling valve has a movable valve bodywhich is acted on in closing direction by pressure in the load-signalingline and in opening direction by an output of the pressure valve; andthat the pressure valve is a pressure reduction valve.
 20. A controlsystem according to claim 18, wherein there is a parallel connectionconnected in parallel with the pressure valve (65) via a load-signalingvalve (20), wherein this parallel connection is selectively closed. 21.A control system according to claim 20, wherein the load-signaling valve(20) of the second compensator has a movable valve body (22) which isselectively moved to a closed position.
 22. A control system accordingto claim 21, wherein the pressure valve (65) is connected to a portionof the second consumer line (12) which is between the variabledisplacement pump (10) and the metering throttle (14).
 23. A controlsystem according to claim 20, wherein the pressure valve (65) isconnected to a portion of the second consumer line (12) which is betweenthe variable displacement pump (10) and the metering throttle (14). 24.A control system for a plurality of hydraulic consumers comprising:avariable displacement pump having a displacement which is adjustable bya load-sensing regulator, said load-sensing regulator being selectivelyconnected with a load pressure by a load-signaling line, wherein saidload-sensing regulator includes a maximum pressure control and a powercontrol; a first and a second adjustable metering throttle, the firstmetering throttle being connected between the variable displacement pumpand a first of the hydraulic consumers, the second metering throttlebeing connected between the variable displacement pump and a second ofthe hydraulic consumers; a first and a second pressure compensator, thefirst pressure compensator being connected behind the first meteringthrottle, and the second pressure compensator being connected behind thesecond metering throttle; wherein each of the pressure compensators hasa regulating piston, the piston of each of a respective one of thepressure compensators being acted on, via a front side thereof, bypressure behind the corresponding metering throttle in an openingdirection, and on a rear side of the piston by pressure in theload-signaling line in a closing direction; a pressure valve connectedwith one of said first and said second consumers, and being switchablebetween an active and an inactive state, and when in its active state,defines a limit pressure lying below a maximum pressure; wherein in theactive state of the pressure valve and upon joint activation of only thefirst and second hydraulic consumers, the load sensing regulator isacted on by a pressure which is dependent on a load pressure of thefirst hydraulic consumer when the load pressure of the first hydraulicconsumer is greater than the limit pressure and said pressure valve isin its active state; and the load sensing regulator is acted on by apressure which is dependent on the limit pressure when the load pressureof the first hydraulic consumer is less than the limit pressure and saidpressure valve is in its active state.
 25. A control system for aplurality of hydraulic consumers comprising: a variable displacementpump having a displacement which is adjustable by a load-sensingregulator, said load-sensing regulator being selectively connected witha load pressure by a load-signaling line, wherein said load-sensingregulator includes a maximum pressure control and a power control;afirst and a second adjustable metering throttle, the first meteringthrottle being connected between the variable displacement pump and afirst of the hydraulic consumers, the second metering throttle beingconnected between the variable displacement pump and a second of thehydraulic consumers; a first and a second pressure compensator, thefirst pressure compensator being connected behind the first meteringthrottle, and the second pressure compensator being connected behind thesecond metering throttle; wherein each of the pressure compensators hasa regulating piston, the piston of each of a respective one of thepressure compensators being acted on, via a front side thereof, bypressure behind the corresponding metering throttle in an openingdirection, and on a rear side of the piston by pressure in theload-signaling line in a closing direction; a pressure valve beingswitchable between an active and an inactive state, and when in itsactive state, defines a limit pressure lying below a maximum pressure;wherein in the active state of the pressure valve and upon jointactivation of only the first and second hydraulic consumers, the loadsensing regulator is acted on by a pressure which is dependent on a loadpressure of the first hydraulic consumer when the load pressure of thefirst hydraulic consumer is greater than the limit pressure and saidpressure valve is in its active state; and the load sensing regulator isacted on by a pressure which is dependent on the limit pressure when theload pressure of the first hydraulic consumer is less than the limitpressure and said pressure valve is in its active state.